The present invention relates to an improved piston for an internal combustion engine which is adapted to create a tumble flow of intake air in the combustion chamber for mainly attaining a stratified charge combustion.
U.S. Pat. No. 6,220,215 B1 discloses a piston for an in-cylinder direct injection gasoline engine which has a recess in the piston crown. Tumble flows of intake air introduced into a combustion chamber in an engine cylinder are created in the recess, and fuel injected into the combustion chamber is entrained on the tumble flows. A stratified charge flow of air-fuel mixture is thus formed and directed toward a spark plug.
However, since the recess of the piston crown in the above-described earlier technology has a plane bottom surface, the following problem tends to occur. If such a piston as described in the above-described earlier technology is employed in an in-cylinder direct injection engine having two intake valves and adapted to create two parallel tumble flows of intake air, the tumble flows will not be adequately adjusted at large flow velocity of the tumble flows under the high-speed engine operation. Cycle variation in flow velocity or turbulence of the tumble flows will be increased, and a flow of air-fuel mixture will be fluctuated to thereby fail to direct the tumble flows toward the spark plug. This causes deterioration of combustion stability of the engine.
There is a demand to solve the above-described problem. An object of the present invention is to improve combustion stability of an in-cylinder direct injection engine by retaining two parallel tumble flows at a stable state from a compression stroke of a piston to a combustion stroke thereof.
According to one aspect of the present invention, there is provided a piston for an internal combustion engine, comprising:
a piston crown having a central axis; and
a piston bowl disposed in the piston crown, on which two tumble flows of air are provided,
the piston bowl having a contour in section taken along a vertical plane intersecting the tumble flows, the contour including an inclined portion inclined toward the central axis of the piston crown, the two tumble flows being disposed at the inclined portion.
According to a further aspect of the present invention, there is provided a piston for an internal combustion engine, comprising:
a piston crown having a central axis; and
a piston bowl disposed in the piston crown, on which two tumble flows of air are provided,
the piston bowl including a bottom wall and opposed and inclined side walls connected with the bottom wall, the side walls being opposed to each other and inclined toward the central axis of the piston crown.
According to a still further aspect of the present invention, there is provided a piston for an internal combustion engine, comprising:
a piston crown including an intake side and an exhaust side; and
a piston bowl disposed in the piston crown, the piston bowl having a generally V-shaped section taken along a vertical plane perpendicular to a direction extending from the intake side of the piston crown toward the exhaust side thereof.
According to a still further aspect of the present invention, there is provided an internal combustion engine, comprising:
a cylinder chamber;
a cylinder head enclosing the cylinder chamber;
a piston within the cylinder chamber, the piston cooperating with the cylinder chamber and the cylinder head to form a combustion chamber;
at least two intake ports in the cylinder head, communicating with the combustion chamber to introduce air into the combustion chamber;
at least two exhaust ports in the cylinder head, communicating with the combustion chamber;
an intake air control valve in each of the at least two intake ports, operative to deflect the air and create two tumble flows of the air in the combustion chamber;
a fuel injector in the cylinder head, operative to directly inject fuel into the combustion chamber;
a spark plug in the cylinder head, operative to ignite an air-fuel mixture in the combustion chamber;
wherein the piston includes:
a piston crown having a central axis; and
a piston bowl disposed in the piston crown, on which the two tumble flows of air are provided,
the piston bowl having a contour in section taken along a vertical plane intersecting the tumble flows, the contour including an inclined portion inclined toward the central axis of the piston crown, the two tumble flows being disposed at the inclined portion.